c++ - WinRT C++中的BitmapImage SetSourceAsync

我是WinRT c ++的新手。我正在尝试从C＃传递StorageFile图像并打开文件，并将其设置为WinRT中BitmapImage中的源，以提取图像的高度和宽度。我正在使用以下代码。

auto openOperation = StorageImageFile->OpenAsync(FileAccessMode::Read); // from http://msdn.microsoft.com/en-us/library/windows/desktop/hh780393%28v=vs.85%29.aspx
openOperation->Completed = ref new
    AsyncOperationCompletedHandler<IRandomAccessStream^>(
    [=](IAsyncOperation<IRandomAccessStream^> ^operation, AsyncStatus status)
{
    auto Imagestream = operation->GetResults();
    BitmapImage^ bmp = ref new BitmapImage();
    auto bmpOp = bmp->SetSourceAsync(Imagestream);
    bmpOp->Completed = ref new
        AsyncActionCompletedHandler (
        [=](IAsyncAction^ action, AsyncStatus status)
    {
        action->GetResults();
        UINT32 imageWidth = (UINT32)bmp->PixelWidth;
        UINT32 imageHeight = (UINT32)bmp->PixelHeight;
    });
});

此代码似乎无效。在BitmapImage ^ bmp =行之后ref new BitmapImage（）;调试器停止说找不到源代码。
您能帮我写正确的代码吗？

最佳答案

我认为您打算写openOperation->Completed += ref new...和bmpOp->Completed += ref new...。我不是C ++专家，但是从我所看到的-异步操作通常包装在create_task调用中。不确定为什么-也许避免在不取消订阅的情况下订阅事件？

我认为它应该大致如下所示：

auto bmp = ref new BitmapImage();

create_task(storageImageFile->OpenAsync(FileAccessMode::Read)) // get the stream
    .then([bmp](IRandomAccessStream^ ^stream) // continuation lambda
{
    return create_task(bmp->SetSourceAsync(stream)); // needs to run on ASTA/Dispatcher thread
}, task_continuation_context::use_current()) // run on ASTA/Dispatcher thread
    .then([bmp]() // continuation lambda
{
        UINT32 imageWidth = (UINT32)bmp->PixelWidth; // needs to run on ASTA/Dispatcher thread
        UINT32 imageHeight = (UINT32)bmp->PixelHeight; // needs to run on ASTA/Dispatcher thread

        // TODO: use imageWidth and imageHeight
}, task_continuation_context::use_current()); // run on ASTA/Dispatcher thread

关于c++ - WinRT C++中的BitmapImage SetSourceAsync，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/25932162/